Nutating antenna assembly



1957 A. P. EDELMAN 2,803,007

NUTATING ANTENNA ASSEMBLY 2 Sheets-Sheet 1 Filed Feb. 29, 1956 an @BQE a 6 mm 7 INVENTOR Aaron I? Ede/man BY M as SG B Q EEQSE S Emma ATTORNEY Aug. 13, 1957 EDELMAN 2,803,007

NUTATING ANTENNA ASSEMBLY I Filed Feb. 29, 1956 2 Sheets-Sheet 2 INVENTOR Aaron R Ede/man ATTORNEYS United Sttes NUTATlNG ANTENNA ASSEMBLY Aaron I. Edelman, Van Nuys, Calif.

Application February 29, 1956, Serial No. 568,617

9 Claims. (Cl. 343-762) The present invention relates to radio detection and ranging systems and more particularly to an improved scanning antenna assembly for use in such systems.

In radio detection and ranging systems of the radar type, a wave signal is radiated from an antenna to be reflected to the radiating station by any object that might lie in its path. It has been found that greater direction sensitivity of the radiated wave may be achieved when extremely high frequencies are used and when the wave is radiated in the form of a conical beam. Such a wave can be obtained by means of a wave guide section as the radiating antenna. It has also been found that the greatest amount of energy is reflected from the intercepting object when the radiated wave from the wave guide antenna assembly has a particular polarization. Therefore, when the conical beam is swept or scanned around a central axis for searching purposes, it is desirable that the polarization of the radiated wave remain unchanged. Therefore, the end of the radiating wave guide section must be moved about a central axis without changing its angular position with respect to its own axis. This motion has been designated as mutation; and when the end of the radiating wave guide section is moved about a central axis without changing its angular position with respect to its own axis, the wave guide is said to be mutated about the central axis.

Prior art systems, for the most part, have attempted to produce nutational motion by converting usual rotational motion into such nutational motion. This, however, has required involved and expensive machines in corporating awkward and cumbersome linkages; which not only render the machines unduly complicated, but which in addition are not susceptible to convenient displacement control of the nutating antenna.

It is an object of the present invention to provide an improved and simplified nutating antenna system, in which the end of a wave guide section is nutated about a central axis by a simple and straight forward driving system that produces nutational motion directly and with out the need for linkages or other cumbersome instrumentalities for converting rotational motion to nutational motion.

Another object of the invention is to provide such an improved nutating antenna system in which the displacement of the end of the nutating wave guide section from the central axis, as well as the path thereof can be simply and conveniently controlled.

Yet another object is to provide such an improved nutating antenna system that does not require bearings or bearing surfaces so that it may be operated in a wide temperature range that exceeds the range in which bearings can normally be operated.

A still further object of the invention is to provide a system that can be constructed to be mechanically resonant at the nutating frequency so as to require a minimum of driving power.

The features of the invention which are believed to 2,803,007 Patented Aug. 13, 195.7

be new are set forth in the claims. The invention itself, however, together with further objects and advantages thereof may best be understood by reference to the following description when taken in conjunction with the accompanying drawing, in which:

Figure 1 is a side elevational view, partly in section, of one embodiment of the antenna assembly of the invention;

Figure 2 is a cross-sectional view of the embodiment of Figure 1 taken along the line 2-2;

Figure 3 is a circuit diagram of an appropriate control for the mechanism; and

Figure 4 is a fragmentary view of a modification of the invention.

The invention provides an antenna system which comprises a wave guide section, a base plate having an aperture therein, and means for pivotally supporting one end of the wave guide section on the base plate in axial alignment with the aperture. A series of resilient rods are each supported at one end by the base plate, and these rods extend outwardly from the base plate. Means is provided for connecting the other end of each of the rods'to the wave guide section resiliently to support the section on a central axis extending outwardly from the base plate. Means is then provided for establishing a dynamic magnetic field around the wave guide section at a position spaced axially from the base plate to cause the end of the section remote from the base plate to nutate about the axis.

Referring now to the drawing and particularly to Figures 1 and 2, it may be seen that the assembly includes a housing 10 of essentially cylindrical shape, and having a base plate 11 supported at one end thereof by means of a series of mounting screws 12. The base plate has a central aperture 13 therein, and a conductor 14 extends through this central aperture. The aperture 13 and conductor 14 form an inlet for the high frequency energy that is to be radiated, and this energy may be coupled to the inlet from any suitable known source (not shown) and by any suitable known coupling arrangement.

The antenna system also includes a coaxial wave guide section having an inner conductor 15 which has an end portion of reduced section extending into the inlet conductor 14 to form a usual high frequency choke joint,

and the wave guide section also includes a hollow outer conductor 16 extending coaxially with the inner conductor 15. The outer conductor 16 has a separate flanged member 17 mounted on the rear end thereof, and one end of a coil spring 18 is affixed to that flange by means of a screw 18, the other end of the spring being clamped to the base plate 11 by means of a screw 19. The spring 18 serves to retain the wave guide 15, 16 adjacent the base plate 11 in pivotal relation therewith with the end of conductor 15 extending into the conductor 14 and with the outer hollow conductor 16 surrounding the aperture 13. This permits the wave guide section 15, 16 to be nutated about a nutating center X without impeding to any appreciable extent the flow of the high frequency energy from the inlet to the wave guide section as it is nutated about a central axis in a manner to be described.

The forward end of the outer wave guide conductor 16 has a cylindrical transfer bracket 20 mounted thereon which forms an annular flange around this conductor. A series of spring rods 21, formed of any suitable resilient material, are each supported at one end in a split sleeve 22 threaded into the base plate 11 and clamped thereby about the corresponding rod. The other end of each of the rods 21 is supported in a similar split sleeve 23 threaded into an annular transfer bracket 24 and clamped thereby on the corresponding rod. A coil spring 25 has one end secured to the bracket 24, and the wave guide assembly 15, 16 and 27.

/ 3 other end of the spring is fastened to the transfer bracket 20 on the wave guide conductor 16.

The wave guide section 15, 16 therefore is pivoted at one end .to the base plate 11, andit extends outwardly from the base plate along a central axis. The section 18 flc-atingly supported on this axis by means of the resilient rods 21. The arrangement is such that the wave guide may be nutated about the central axis and the nutating center X.

The Wave guide section 15, 16 projects beyond the transfer bracket 20 to the forward end of the housing 19, and the section is connected at its free end to a usual transition block 26 which electrically couples the wave guide section 15, 16 to a rectangular wave guide radiating element 27. The radiating element 27 projects through an enlarged aperture in the end ofhousing and outwardly beyond the end of the housing. The transition block 26 carries an annular shell26' which covers the aperture as the wave guide section 15, 16 and 27 is nutated. The radiating element 27 is of known configuration so as to radiate a high frequency wave in the form of a conical beam, and this antenna is nutated in a manner and by means that will now be described.

A second series of resilient rods 28 each have one end mounted in the base plate 11 by the same type of sleeves as the rods 21, and the other end of each of the rods 28 extends in a corresponding sleeve through a cylindrically shaped bracket 29 which is positioned coaxially of the transfer bracket 24. The bracket 29 supports a driving coil assembly 30 which surrounds the outer conductor 16 of the wave guide section 15, 16 at a position spaced axially from the base plate. The portion of the wave guide conductor 16 that is surrounded by the driving coil supports a magnetic member 31; which member may be a cylindrical shaped permanent magnet body mounted coaxially with the wave guide conductor 16 and which 'is longitudinally magnetized, or a coil wound about the longitudinal axis of the wave guide section and having direct current flowing therethrough to produce a static magnetic field.

The driving coil 30 may be similar to the stator of a typical three phase synchronous motor or have any other known form to produce a rotating magnetic field. When the driving coil 30 is energized by a three phase current, the dynamic rotating magnetic field reacts with the static field from the magnetic member 31 to deflect that member away from the central axis. Due to the fact that member 31 is longitudinally magnetized there is no tendency for that member to rotate, instead it is deflected around the central axis with a fixed angular position with respect to its own axis, this being the desired nutational motion. Since the forces produced act between the two members 30 and 31, these members are deflected in the opposite direction on opposite sides of the central axis. Therefore, the rotating magnetic field of the driving coil 30 causes the wave guide antenna assembly to nutate and at the same time to produce equal and opposite nutation of the driving coil.

It is desirable that the system be designed so that the magnetic force exerted on the wave guide assembly by the driving coil 30 is at the center of percussion so that the members and 16 will have a natural tendency to pivot at the nutating center X. This precludes any tendency for radial motion at the joint between the inlet 13, 14 and the conductors 15, 16 during nutation of the wave guide, so that these members may be maintained in the desired aligned positions by spring 17 without impeding the nutating action.

Itis also desirable that the system be dynamically balanced by making the moment of the driving coil 36 about the base plate 11 equal to the moment of the Moreover, the spring constants of the resilient rods 21 and 23 can be adjusted by rotating the split sleeves in the base plate 11 and in the brackets 24 and 29 to control the effective member length of these rods. The spring constants are preferably adjusted so that the driving coil assembly and the wave guide assembly are nutated at their natural mechanical frequency for optimum transfer of driving force into the notational motion. When this is done, a relatively small amount of driving power produces sizable deflection and mutational motion.

The control system of Figure 3 includes a usual electronic control unit which is constructed in a known manner and whose function is to respond to electrical control signals to control the amplitude of the three-phase current supplied to the driving coils 30. To this end, the unit 50 is connected to any suitable source of three phase power by way of leads 51 and to the driving coil 30 by leads 52. Various control signals for unit 50 are received over leads 53. For example, certain of the leads 53 may be connected to a manual control panel so that the amplitude of the three phase current supplied to the driving coils 30 over leads 52 may be manually controlled to control the amount of deflection of the antenna 27. When magnetic member 31 is a coil having direct current flowing therethrough, the amount of deflection of antenna 27 can also be controlled by controlling the value of this current. Also, certain programing signals can be received over others of the leads 53 so that the deflection of the antenna 27 can be controlled in accordance with any desired pattern which may, for example, be determined by reflected signals received by the antenna 27.

The nutating path of the antenna may be conveniently controlled by the unit 50 by connecting the unit over a pair of leads 54 to a usual deflection sensing unit 55 which is mechanically coupled to one of the resilient rods 28. The unit 55 produces an electrical control which is a function of the deflection path of the adjacent rod 28, and this control is applied over leads 54 to the unit 50 so as to control the three phase current supplied to the driving coils 30. In this manner, the current supplied to the driving coils may be controlled so that the antenna 27 nutates in a circular path or along a path having any desired configuration as determined from the setting of the sensing unit and by the programing signals. Appropriate indicating apparatus for indicating the position of the antenna 27 at any time on its nutating path may be connected directly to the leads 51 from the three phase source over leads 56. Since the deflection of the antenna at any time is directly related to the current from the source, there is no possible ambiguity and this enables the indicating apparatus to be connected directly to the source.

In the modification of Figure 4 the antenna 16, instead of being linked to the transfer bracket 24 through the spring 25 and bracket 20 as in the embodiment of Figure 1, extends through a somewhat spherical shaped bearing 60. The bracket 24 of Figure 1 is represented as 24 in Figure 4, and this bracket is supported by the spring rods 21 as in the previous embodiment. An annular retainer member 61 is aflixed to the bracket 24' and surrounds a bearing ring 62 for the spherical member 60, which ring may be composed of nylon or other suitable bearing material. The ring 62 has an oil reservoir 63 formed therein which is sealed by a gasket 64 of neoprene or other suitable gasket material. The assembly is held in place by an annular retainer 65 Which is threaded to the retainer 61.

With the assembly of Figure 4, the wave guide 16 is firmly retained and mechanically coupled to the resilient rods 21 for nutation about the nutating center in the manner previously described.

The invention provides, therefore, an improved nutating antenna system which is relatively inexpensive and of light weight, and in which nutation is obtained directly by means of a simplified system and not by an attempt to convert rotational motion into nutational motion through cumbersome and complicated linkages. Since all of the elements of the system nutate there is no need for bearings or rubbing parts, and this renders the system independent of temperature for all practical purposes and enables it to be operated at low temperatures at which the prior art systems would require prohibitive initial driving forces due to the sluggishness of the bearings. The system is easy to control since the nutating ofiset of the antenna elements can be varied merely by varying the electric current through the driving coil. Also, the nutating path can be set to have any desired configuration by means of the control circuit described herein.

Although the now preferred embodiment of the present invention has been shown and described herein, it is to be understood that the invention is not to be limited thereto, for it is susceptible to changes in form and detail within the scope of the appended claims.

I claim:

1. An antenna assembly including in combination: a wave guide section; means for resiliently supporting said wave guide section on a central axis; and means for establishing a dynamic magnetic field around said wave guide section to cause an end thereof to nutate about the central axis.

2. An antenna assembly including in combination: a wave guide section; a base plate; means for pivotally supporting one end of said wave guide section on said base plate; resilient means for floatingly supporting said wave guide section on a central axis extending outwardly from said base plate; and means for establishing a dynamic magnetic field around said wave guide section to cause the end thereof remote from said base plate to nutate about said central axis.

3. An antenna assembly including in combination: a wave guide section; a base plate having an aperture therein; means for pivotally supporting one end of said wave guide on said base plate in axial alignment with said aperture; a series of resilient rods each supported at one end by said base plate and extending outwardly from said base plate; means for connecting the other end of each of said rods to said wave guide section on a central axis extending outwardly from said base plate; and means for establishing a dynamic magnetic field around said wave guide section at a position spaced axially from said base plate to nutate said section about said central axis.

4. An antenna assembly including in combination: a wave guide section; a base plate having an aperture therein; means for pivotally supporting one end of said wave guide section on said base plate in axial alignment with said aperture; a series of resilient rods each supported at one end by said base plate and extending outwardly from said base plate; means for connecting the other end of each of said rods to said wave guide section resiliently to support said section on a central axis extending outwardly from said base plate; means for establishing a dynamic magnetic field around said wave guide section at a position spaced axially from said base plate; and a member for establishing a static magnetic field afiixed to said wave guide section and positioned to. lie in said dynamic magnetic field to be moved thereby and cause the end of said wave guide section remote from said base plate to nutate about said central axis.

5. The antenna assembly defined in claim 4 in which said last named member comprises an inductive winding wound about the longitudinal axis of said wave guide section for establishing a static magnetic field.

6. The antenna assembly defined in claim 4 in which said magnetic member is a longitudinally magnetized cylindrical permanent magnet mounted coaxially with said wave guide section for establishing a static magnetic field.

7. The antenna assembly defined in claim 4 in which said dynamic magnetic field is established around said wave guide section at the percussion center thereof with respect to the end thereof pivoted on said base plate.

8. An antenna assembly including in combination: a wave guide section; a base plate having an aperture therein; means for pivotally supporting one end of said wave guide on said base plate in axial alignment With said aperture; a first series of resilient rods each supported at one end by said base plate and extending outwardly from said base plate; means for connecting the other end of each of said rods to said wave guide section resiliently to support said section on a central axis extending outwardly from said base plate; a driving coil for establishing a dynamic magnetic field around said Wave guide section at a position spaced axially from said base plate; a second series of resilient rods each supported at one end by said base plate and extending outwardly from said base plate; means for connecting the other end of each of said rods of said second series to said driving coil resiliently to support said driving coil coaxially with said wave guide section; and a magnetic member affixed to said wave guide section and positioned to lie on said dynamic magnetic field to be moved thereby to cause said driving coil and the end of said wave guide section remote from said base plate to nutate about said central axis.

9. The antenna assembly defined in claim 8 which includes means for individually adjusting the effective lengths of said resilient rods of said first and second series to control the spring constants thereof so that the system may be brought into mechanical resonance with the nutating frequency.

No references cited. 

